The invention relates to a method for reducing the effect of disturbance signals in a system including a transponder and a reader.
The invention further relates to an identification system comprising at least one transponder and at least one reader.
Transponders are electronic circuits containing information used for identification of animals, for identification of any type of object, for attaching dedicated information to any type of item in logistics processes, etc. Transponders are used in combination with a reader device which communicates with said transponder and makes the information stored in the transponder available to the user of said information. In certain cases there is also the possibility that said reader device sends information to the transponder, where said information may also be stored in the transponder memory (Read-Write systems, etc.). Typically, transponders have little energy at their disposal for internal handling of their information (e.g. read/write operations) and for transmitting the required information to the interrogating reader device: So-called active transponders have an internal energy source (a battery or the like) which, however, usually is quite small due to size, weight and cost restrictions, while so-called passive transponders do not have an internal energy source but make use of the energy of the interrogating field.
While the problem solved with this invention is of prime interest for passive transponders, also active transponders may benefit: Due to the very limited energy received by the interrogating reader from a transponder, a consequence of the above outlined internal energy restriction within the transponder, the reception of the information transmitted by the transponder is prone to be disturbed by sources of disturbance in the environment of an interacting system comprising a transponder and a reader. If the frequency of a disturbing signal is very close or even identical with the frequency of the signal provided by the transponder to transmit information to the interrogating reader, the reader may not be able to properly assess this information. Since the energy level of the signal received by the interrogating reader from the transponder is rather low, reception of such a signal can easily be disturbed even by relatively weak disturbance sources. In real world applications such a disturbance often significantly decreases the achievable reading distance between transponder and reading device, sometimes even down to almost zero, thereby heavily compromising the transponder system performance.
In view of the foregoing the main aim of the instant invention is to provide a method and a system for substantially reducing the negative effect of disturbance signals on the operation of a system comprising a transponder and a reader.
According to a first aspect of the invention this aim is attained with a method comprising emitting a signal from the transponder, receiving the signal emitted by the transponder in a reader having a first receiving unit and having a second receiving unit, wherein the energy levels of the transponder signals which are received by the first and second receiving units are substantially different. A disturbance signal emitted by a disturbance source is received by both of the first and second receiving units. The energy levels of the disturbance signals which are received by the first and second receiving units are substantially the same. Based on the foregoing, a first output signal is provided from the first receiving unit and a second output signal is provided from the second receiving unit. Each of the first and the second output signals comprises a transponder signal component and a disturbance signal component. The output signals of the first and second receiving units are combined, thereby generating a third output signal, which comprises a transponder signal component which is much larger than a disturbance signal component of the third output signal.
According to a second aspect of the invention this aim is achieved using an apparatus which performs the method, including at least one transponder which emits a transponder signal, at least one reader having at least a first and second receiving unit, each for receiving the transponder signal and each of the receiving units is also able to receive a disturbance signal that is emitted by a disturbance source. The receiving units are so arranged with respect to the transponder that the energy levels of the transponder signals received by the first and second receiving units are substantially different. The receiving units are arranged with respect to the disturbance source so that the energy levels of the disturbance signals which are received by the first and second receiving units are substantially the same. The first receiving unit provides a first output signal and the second receiving unit provides a second output signal. Each of the first and second output signals comprises a transponder signal component and a disturbance signal component. There are means for combining the output signals of the first and second receiving units for generating a third output signal comprising a transponder signal component, which is much larger than a disturbance signal component. The receiving units may comprise coils, and their windings and the mode of attachment determine how they perform with respect to each other.
The main advantage of the invention is that it makes possible to practically eliminate the influence of disturbing signals, to improve substantially the performance of a transponder reader system, and to increase the operating distance between reader and transponder in such a system.